Field
The present disclosure relates to an OCT data processing method for OCT data acquired by optical coherence tomography, a storage medium storing a program for executing the OCT data processing method, and a processing device.
Description of the Related Art
As a method of acquiring a tomographic image of an object to be inspected, for example, a living body, in a non-destructive and non-invasive manner, optical coherence tomography has been put into practical use. An OCT apparatus for executing the above-mentioned method, which is capable of acquiring a tomographic image of an object to be inspected, for example, a retina in a fundus of an eye, is widely used for ophthalmologic diagnosis of the retina or the like.
The OCT apparatus is configured to cause light reflected from the object to be inspected and reference light to interfere with each other, and analyze time dependence or wavenumber dependence of an intensity of the interference light, to thereby acquire a tomographic image. As such OCT apparatus, there are known a time domain optical coherence tomography (TD-OCT) apparatus, a spectral domain optical coherence tomography (SD-OCT) apparatus, and a swept-source optical coherence tomography (SS-OCT) apparatus. The TD-OCT apparatus is configured to acquire depth information on the object to be inspected by changing an optical path length of the reference light by moving a reference mirror. The SD-OCT apparatus is configured to acquire the depth information by using light emitted from a broadband light source. The SS-OCT apparatus is configured to acquire the depth information by using light emitted from a wavelength-tunable light source capable of changing an oscillation wavelength. The SD-OCT apparatus and the SS-OCT apparatus are collectively referred to as “Fourier domain optical coherence tomography (FD-OCT) apparatus”.
In recent years, there has been proposed simulated angiography using the FD-OCT apparatus, which is referred to as “OCT angiography (OCTA)”. In fluorescence angiography, which is general angiography in contemporary clinical medicine, injection of a fluorescent dye (for example, fluorescein or indocyanine green) into a body is required. A bright region through which the fluorescent dye passes is imaged, to thereby display a vessel two-dimensionally. However, a contrast medium may produce side effects including nausea, eruption, and coughing, and may cause shock symptoms on rare occasions. Hence, angiography involves some risks. Meanwhile, OCTA enables non-invasive simulated angiography without a risk of injecting a foreign matter into the body, and enables three-dimensional display of a network of vessels. In addition, OCTA is attracting attention because OCTA is higher in resolution than fluorescence angiography and can visualize minute vessels or blood flow of the fundus.
As OCTA, there are proposed a plurality of methods depending on a difference in manner of detecting a vessel region. For example, in Fingler et al. “Mobility and transverse flow visualization using phase variance contrast with spectral domain optical coherence tomography” Optics Express. Vol. 15, No. 20. pp. 12636-12653 (2007), there is proposed a method of extracting only signals with time modulation from interference signals acquired by the OCT apparatus, to thereby separate the interference signals caused by the blood flow. There are also proposed a method utilizing phase fluctuations due to the blood flow (“Speckle variance detection of microvasculature using swept-source optical coherence tomography” Optics Letters Vol. 33, No. 13, pp. 1530-1532 (2008)), a method utilizing intensity fluctuations due to the blood flow (Mariampillai et al., “Optimized speckle variance OCT imaging of microvasculature,” Optics Letters Vol. 35, No. 8, pp. 1257-1259 (2010) or U.S. patent Application Publication No. 2014/221827), and the like.
Currently, in medical sites, an examination of hypertension or the like places an importance on observation of a change in hypertrophy of the vessel, which leads to arteriosclerosis, and there is a demand to acquire information relating to the hypertrophy of the vessel, that is, information on a vessel wall by a simple method.